Magnetic resonance imaging (MRI) techniques make use of electromagnetic fields to create images of a patient. MRI techniques permit the generation of high-quality two- or three-dimensional images of a patient's body, which can then be examined by a physician for diagnosis purposes. In particular, MRI techniques permit the generation of internal images of a patient's flesh, blood, bones, cartilage, blood vessels, organs, and the like. The generated images can then be examined by physicians in order to diagnose disease, disorders or injuries, and facilitate patient care.
MRI devices typically subject a patient to a very strong static magnetic field and a pulsed gradient magnetic field, and then apply pulses or bursts of electromagnetic radiation (typically radio frequency (RF) radiation bursts) to an area of the patient to be imaged. The strong magnetic field generally orients the protons of the patient's tissue in particular directions. However, the RF radiation bursts cause some of the patient's protons to resonate, or spin, at a particular frequency depending on the local magnetic field during application of the radiation burst. The resonance frequency in MRI is referred to as the Larmour frequency which has a relationship with the local magnetic field. When the RF radiation burst is terminated, the resonating protons reorient themselves in accordance with the strong magnetic field of the MRI device, giving off energy in the process. The MRI device can detect the energy given off by the reorienting protons in order to create a high quality image of the patient's tissue.
In some cases, application of the RF radiation bursts must be timed specifically with a patient's physical body rhythm. For example, when using MRI to image a patient's heart, each burst should be timed for application at a common point of the sinus rhythm. In other words, each of a series of MRI electromagnetic radiation bursts and gradient fields may need to be applied when the heart is in a similar state, i.e., in the same stage of the cardiac cycle. In order to monitor or measure the condition of the heart to facilitate timing of the electromagnetic radiation bursts, MRI techniques typically make use of surface electrocardiograms (ECGs). The ECGs provide measurements of the sinus rhythm and thereby facilitate the coordination of electromagnetic radiation bursts at common times during the cardiac cycle. Surface ECGs, however, can sometimes provide inaccurate cardiac measurements. Moreover, the electromagnetic radiation bursts used for MRI may significantly affect ECG readings such that accuracy of the measurements are undermined during the MRI.